By the way, the latest intercept was of a 1500km MRBM, not 2000km. Sorry for my mistake before. 1500km MRBM have typical speed at 15km altitude (not 20km) of 5Mach.Here is the link. States 30km outside atmosphere.
India’s Advanced Air Defense Interceptor Destroys Incoming Ballistic Missile in Test
Nah, it doesn't slow down that much. Mach 5 is typical for 300-400km SRBM.
I don't think India has tested MRBM of higher range against AAD yet.