Check out Alliant Powder's site. They have loads for both 69 and 77 grain SMKs, but not for the 80 grainers.
Load Data has several loads for the 80 grain SMKs, from 22 to 24 grains of powder with an OAL of 2.550". This may not work in your gun, but it is listed for use in a 1 in 7" twist rifle.
Perhaps this will help, but the fast answer is yes you can load all three weights with RL 15. Now, the thing is, will your rifle like the loads? Only range time can answer that question.
Good luck, and have fun finding out.