Yes it is possible and you can easily install 29-inch wheels on 27.5-inch forks, but although it is not recommended or a compatible setup because there are many bike components, the bike wheel and fork need proper compatibility. this setup is only possible for those riders who are taller in height and whose feet are much longer in length, because this setup is also going to raise the bottom bracket of your bike, and if you are smaller in height then it would be difficult for you when you want to stop or take your foot on the ground, you will not be able to touch your feet with the ground surface of trails, it happens due to the difference in hi=eight of the bottom bracket.
Mostly this setup is worth and better for mountain biking, smaller tires do not cover the large distance on the ground when the crankset completes one revolution as compared to larger 29 wheels, larger wheels have a big advantage with the smaller 27.5 forks or frames, and larger wheels would cover greater distance when you complete one rotation of the chain ring, an also single trails are hard and rough and contains many long grown trees, bushes, smaller and bigger rocks, these trails would sometimes block the way of the smaller sized wheels but longer wheels would easily cross them and make their way for going ahead.
29-sized wheels on smaller-sized 27.5 forks do not play a major role in increasing MTB speed, if you calculate the total speed difference3 then you will get to know, just 3 to 4% of your bike speed is increased with 29 wheels on smaller-sized forks a compared to previous 27.5 wheels.
There is a large weight difference between 27.5 and 29 wheels, so larger sized wheels are going to add much more weight to your bike, and if you are a pro experienced racer, then this setup is not going to help you or it is not in favor for you, the larger weight of the wheel would also play a major role in decreasing bike speed, it is the reason that speed of the bike is going to increase so much with this setup.
Rotating Of Wheel And Pedalling:
When you install a larger 29 wheels in a smaller 27.5 fork then you will feel a large noticeable difference in pushing of your bike pedals with this setup, you have to apply a larger force with more power and capacity, it only happens because the setup is not specific and 27.5 forks are not exactly made for larger 29 wheels, 29 wheels will rotate with a larger force and you will feel that your wheels are much heavier, including the wheels when you ride with the same bike on terrains you will clearly notice that your whole bike heavier, you will lose all of your previous riding training and skills riding because the handling of the bike is also changed too much with the new setup.
Friction And Resistance:
This setup is only beneficial regarding friction and rolling resistance. 29 wheels have lesser friction and resistance with the smaller sized 27.5 forks and also better rolling when these wheels roll on rough terrains, you have to push pedals with a larger force, and the tires continuously roll over the trails with slipping or skidding and do not cause any friction or rolling resistance.
Difference In Tire Width:
There is a big difference between the width of the smaller sized 27.5 and larger sized 29 tires, these 29 tires are wider and thicker in their width as compared to 27.5 tires, so if you are installing 29 tires within the smaller sized 27.5 forks then you have to change or replace 29 wheel tires, to replace the width and thickness of these tires, you have to find or buy thinner or slick tires so that these tires would easily install within the 27.5 forks and becomes compatible without any trouble and issue.
27.5 wheels have 23mm of width and 29 wheels have 24.5mm of width, there is a difference of 1.5millimeters, you have to make this difference of tires and wheels compatible with the dropout spacings of the fork and the hub axles, if the axle is smaller in length then you have to replace hub axle, but if the axle has longer length then insert the spacers or washers on both drive and non-drive side of the front and rear wheel.
27.5 And 27.5+(Plus) Forks:
There is a larger noticeable difference between 27.5 and 27.5 plus bike tires. 27.5 bike tires are thinner in diameter and 27.5+ bike tires are thicker and wider in diameter, which means 27.5 tires have thinner and narrow forks but 27.5+ have thicker and wider forks with greater dropout spacing and distance.
If you have 27.5 normal bikes and you have installed 29 wheels in 27.5 forks then you need thin and slick tires or if you have a 27.5+ bike then their forks would easily adjust larger 29 wheels with greater width tires without any issue.
Downhill And Uphill Trails:
Larger-sized wheels installed in the smaller-sized forks and frames would wobble continuously at higher speeds, due to the non-compatible setup, due to being heavier in weight and greater size, when you are coming down on downhill trails the speed of your bike goes much higher and it would be difficult to keep the handlebar of your bike in a straight forward position, front and rear tires along with the wheels are constantly moving right and left side of the trails, but when you are climbing up to the mountains with the same setup then you will feel a little bit of benefit due to their size, so this setup is beneficial for uphills and not good for downhills.