Leds can draw max 150 mA at 1 Khz 1:10 duty

If you multiplex the data on the 7-segment display you need a bus of seven lines ( the segment information) and one line to activate each display.
If the max. current per led is 150 mA at a duty 1:10 that means that the led brightness will be ( as some old siemens app. note state) equivalent to the same bright as if you supply the led with 15 mA continuous.
If you have 20 display and if you want to maintain the brightness then you will need to multiplex 1:20 but at a 300mA.
The problem is that the led data sheet state a maximum current ( that I understand is 150mA) so know you need two buses of 7 line, one for the first 10 display @1:10 150mA and a second for the next 10. This will consume more hardware.

Daniel