Not necessary. And impossible to say how your gaps will mesh without hitting every club on a launch monitor and in real life. Loft only is not a hard and fast rule when mixing and matching very different heads. Personally, I don't see a reason to mix T100 and T150, especially in the mid irons. If you're gonna do a blended set, stick with the same 5 or 6-P and possibly go to something higher launching in the longer irons if you need the help.

Mixing a set you aren’t fit for is a hard resell if it is a mistake. Get fit for when your next lower club doesn’t provide the launch, spin, or descent angle for an optimal shot. The Titleist sponsored fittings are free with a purchase and their goal is getting it right for you. Mixed or straight set that is optional for you.

Difficult to do a fitting online. I would recommend you go see a certified fitter, for best results. Get the right heads, shaft, grips, lie and lofts. You will never regret it.

Comb sets are a great alternative but you're putting the cart before the horse. I don't know anybody who has a combo set that wasn't on the advice of a fitting.