You can use the Arnold log to check what mip levels are used. In the Image file statistics, there’ll be a MIP-COUNT for every texture

00:00:02 124MB | Image file statistics:
00:00:02 124MB |       opens tiles MB read --redundant-- I/O time res             File
00:00:02 124MB |     1   1   538   12.6                  2.2s     8192x8192x3.f16 debug.tx MIP-COUNT[0,13,314,147,40,15,4,1,1,1,1,0,0,1]
00:00:02 124MB |

For example, with my debug texture, I see

MIP-COUNT[0,13,314,147,40,15,4,1,1,1,1,0,0,1]

in the Arnold log for this render: