## Yes.

Mirage Arcane is a spell that is 7th level.  That is higher than first.  Malleable Illusions would work on it. The dome is one object, so it can be made real for 1 minute. All seems legit.

## And, it isn't as OP as it seems.

That might seem like it is OP, but at level 14 the things your fighting should be able to break through a 27 HP wall in an action or two.  Moreover, that isn't their only way out.

 - Dig
 - Etherealness
 - Dispell
 - Counter Spell
 - etc. etc. etc.