** Using the source for reference to the MM74H148 8 line to 3 line encoder,
the connections for a 16 line to 4 line encoder will be described.
Three 2 input OR gates are required.
Call the lower priority encoder Encod1, and the higher one Encod2.
The 2 output A0's go to one OR gate to become the final A0 output.
The 2 output A1's go to a second OR gate to become the final A1 output.
The 2 output A2's go to the third OR gate to become the final A2 output.
The GS of Encod2 becomes the final A3 output.
When one or more lows are input to Encod2 it disables Encod1,
by connecting E0 of Encod2 to E1 of Encod1.
Connect the fixed enable; E1 of Encod2 to logic '0'
0 to 7 of Encod1 are the final 0 to 7 lower priority inputs.
0 to 7 of Encod2 are the final 8 to 15 higher priority inputs
The same principle will apply even if you use a different chip.
Please ask should any clarification be required.