I dont use musk xylene (it is banned in Europe) so cant comment on that one but musk ketone is certainly a pain to dissolve. 1.5% does seem too weak to me - I keep mine at 10% which is achieved using half benzyl benzoate and half ethanol (to 20% with BB first and then dilute to 10% with ethanol).
According to the Good Scents page on musk ketone
these solvents will dissolve to this extent:
8.9% methyl carbitol
25.4% benzyl benzoate
16.5% diethyl phthalate (DEP)
18.6% dimethyl phthalate
1.8% alcohol (95%)
In practice I find it still needs ages on the automatic stirrer though - more than 24 hours anyway - in fact as I remember the last time I did it I lost patience waiting for all the crystals to dissolve in the benzyl benzoate and doubled the volume with ethanol to hasten it along, which worked. I didnt use any heat so I dont know whether that would have helped or not.
BTW - David - Ive never made a scent for a fabric conditioner, but your comment made me wonder if musk ketone would be amplified in the same way when use in an alcohol base perfume if it was sprayed onto clothing: most things last better on clothes than on skin, but that might result in a significantly altered fragrance if it worked exceptionally strongly with MK - do you know whether that is the case?