Undemanding heterosexual prop (15)
I believe the answer is:
straightforward
'undemanding' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'heterosexual prop' is the wordplay.
'heterosexual' becomes 'straight' (similar in meaning).
'prop' becomes 'forward' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'straight'+'forward'='STRAIGHTFORWARD'
Can you help me to learn more?
(Other definitions for straightforward that I've seen before include "That's simple" , "Frank" , "Right on!" , "Plain sailing" , "Clear" .)