Audio buffers = latency. More and/or bigger buffers = more latency, so in plain english: Raise your latency. :) (Or if it's already very high (like >1024 samples) try lowering it. In rare cases Reaper doesn't like too large buffers either.) Also, since you're on a laptop, turn off the build-in WLAN card and the wired network adapter since they can cause the same problems.