The teachings of Je TsongKhapa is directed towards those who
have gd foundation in Buddha teachings
although the basic tenets of Buddha teachings is there , one may be
overwhelmed by the special terms used inside the teachings
My advise is
understand the 4 Noble Truth , Noble Eightfold Path , 12 dependent
Originations , 6 Realms of existence , Rebirth and Karma before
embarking on the whole teachings on Lam Rim
For a beginner to Buddhism , the minimum I will suggest is a total
of 3 years plus meditation or chanting practice ,with unwavering
faith in Buddha Sakyamuni teachings