Shimano crankset with FSA bottom bracket?
If you have the FSA MegaExo crankset it should have a 19mm axle diameter. The Shimano Ultegra FC-R8000 has a 24mm axle. Measure your current crankset’s diameter but you’ll probably need a new bottom bracket for the 24mm axle.

If you’ve ridden a considerable distance (something like >7Mm) on your current bearings it doesn’t really hurt to replace this 10€ part in any case.