Good advice. 4 Hrs vs 15 Hrs seems like a no-brainer to me. It's your performance in Sim assessments that gets you hired. Don't be scared of an extra IR test, you're entering an industry where you will essentially be doing an IR test at least every 6 months until you retire. They are very simple once you understand them - he basically has a checklist of maneuvers he needs to see and you show him one at a time. A multi engine plane flies just like a single engine one, a bit faster perhaps but the instruments are the same. The single engine work is different obviously but there's nothing inherently hard about banging some rudder in, trimming, identifying and securing the engine.
Schools are there to make money, not help you save money. Ultimately you have to put your foot down, tell them what you want and give then the option to help you or lose your business.