Here’s the exact quote:
Do you realize the bullet out of an AR-15 travels five times as rapidly as a bullet shot out of any other gun …?
The muzzle velocity of an AR-15 (which is to say, the speed at which the bullet travels when it leaves the rifle) is about 3300 feet per second (here’s an anti-AR-15 Washington Monthly article confirming that). Other rifles have muzzle velocities in the same general range, 2500-4000 feet per second or so according to this list, or 2700-3150 in this list (PDF p. 45), though the velocity is also influenced in some measure by barrel length. If the AR-15 bullets are faster than most rifles (not “any other” rifles), they’re only slightly faster.
One can say what one will about whether banning AR-15’s is likely to reduce deaths. (I doubt that it will, either for mass shooting deaths or homicide deaths more generally.) But it seems pretty clear that President Biden’s argument for why it would do so is not correct.