Advice on balancing D&D 3.5 feat

[Deremir]

I've had an idea for a feat for a while now and I would like the playgrounds advice on how best to balance it.

Compound Casting [Metamagic]
Prepare two spells as one
Prerequisites: Quicken Spell, Able to cast arcane and divine spells
Benefit: When preparing spells you may prepare two spells as one. They only take up one spell slot of the highest spell level used in the compound spell, and are cast simultaneously. However, both spells must target, or in the case of area of effect spells be centered on, the same object, individual or area, and casting a compound spell takes a full round action provoking an attack of opportunity. Spells with a casting time longer than one round can not be used in a compound spell. Only spells of a spell level one half the highest spell level a wizard of your same level is able to cast (rounded down) can be used for a Compound spell.

For example a wizard 5/ cleric 5 with this feat could cast a compound spell consisting of Silence and Ghoul touch (so long as the silence was centered on the person receiving the ghoul touch) since a level ten wizard can cast 5th level spells and Silence and Ghoul touch are both second level spells.

The intent of this feat is to make a multiclass caster focused on casting many low level spells viable. (in my case I want to play a wizard/cleric/druid for maximum spell options)
Advice is greatly appreciated

[Nifft]

Half a Cleric 5 (rounded down) can't cast Silence, and half a Wizard 5 (rounded down) can't cast Ghoul Touch, but that's just a technical detail.

A deeper issue is that it's unrealistic to balance against a very poorly built character like a Wiz 5 / Clr 5.

For an unoptimized game, you'd want to balance against a Wizard 3 / Cleric 3 / Mystic Theurge 4.

For a more usual game, you'd want to balance against a Wizard 1 / Cleric 3 / Mystic Theurge 6.