They usually provide hotfixes for both. But if the solution to some of your lag is already implemented in 1.5.10 then no. That is why there is a beta version, when 1.5.11 or whatever comes out, 1.5.9 will be updated with the fixes (of 1.5.10).
Also, make sure to report your lag/problem in the tech forum if it is not already reported; your instability does not necessarily translate to other people so it may not apply to everyone