The speed you reading is for the WiFi, not the actual DSL line speed,
Shouldn't give you any issues,
Unless you going to 20Mbps or 40Mbps, which is VDSL, totally different technology in which case you'd need a new router.
Also 4 megs is 37.5 times slower than 150 megs so will definitely work, but if you wanted a gigabit line then you would needed 1 gig or higher wireless if it is possible