You can fit a tpc+ in there. The cartridges are very similiar. You'll probably have to call Manitou to get details and then order it through your local bike shop.
Don't know about the 150mm ti coil. but I can tell you that I've swapped 130mm ti and steel coils on my firefly and I couldn't tell the difference in weight. wouldn't be worth the money, IMO. I would spend the $ on lighter tires or rims if you're trying to save weight.
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