I am loading from Panasonic P2 cards MXF-files shot in AVC-intra 100 into FCP X- and it takes ages, it’s that normal? How can I do it more efficient?

You must have shot a long duration film on your card, you should provide more clues. But if you want to be easy to do it, you can try convert your AVC-intra 100 files to FCP preferred ProRes codec, Pavtube MXF Converter for Mac is a good choice for you.
http://www.pavtube.com/mxf-converter-mac/