Hi,

Are you really trying to count stuff across sheet1 & sheet2? or is that a typo and all the data is on the same sheet (either sheet1 or sheet2)?

If the data is on two sheets and unless it's effectively an OR condition meaning you can add two COUNTIFS together then I don;t believe there's any straightforward way to have an effective AND Countif function across a 3D range.

The Sheet2 COUNTIF alone would be

Formula: copy to clipboard 
=COUNTIFS('Sheet2'!$V$2:$V$445;">=15",'Sheet2'!$V$2:$V$445;"<=30")