DS's English teacher had them pick 7/15 poems, in a way that they had 2 per theme. Then, if one of the memorised poems comes up, you've still got another relevant one to compare it to.
It is still memorising poetry, but its only 7, not 15.
What difference anyway? You've got to memorise things in every subject : formulae, facts and figures. Its all memory, not just the poems and Eng Lit quotes.