Without knowing the details I would say, no, that's not too high, nor a worrying result.
It's very well known that in plants you often have a substantial amount of duplicated genes, and 10% is not high in that respect. If there is some redundancy in your assembly that can also increase the amount of the duplicated fraction but again, I don't think that 10% is very high.
Bottom line, to me this is a totally accepted value/result of the BUSCO analysis.