Running Tumbleweed Calc (LibreOffice 5.2.2.2.0), creating a blank sheet and
opening the dialog takes ~30 seconds.
I've tried to do a perf record, but can't see anything obvious:

    10.24%  soffice.bin      libc-2.24.so                             [.]
_int_free
     9.48%  soffice.bin      libc-2.24.so                             [.]
malloc
     7.31%  soffice.bin      libc-2.24.so                             [.]
_int_malloc
     6.37%  soffice.bin      libuno_sal.so.3                          [.]
rtl_uString_release
     3.85%  soffice.bin      libfontconfig.so.1.9.2                   [.]
0x000000000001acdf
     3.32%  soffice.bin      libuno_sal.so.3                          [.]
rtl_uString_assign
     2.48%  soffice.bin      libuno_sal.so.3                          [.]
rtl_uString_acquire
     2.20%  soffice.bin      libuno_sal.so.3                          [.]
rtl_string_release
     2.04%  soffice.bin      libfontconfig.so.1.9.2                   [.]
0x000000000001acc4
     1.99%  soffice.bin      libc-2.24.so                             [.]
__strchr_sse2
     1.89%  soffice.bin      libmergedlo.so                           [.]
GetEnglishSearchFontName