Hi Thierry,
As I know, the Ericsson BSC paging capacity is very high compared to Siemens BSC.
As I know in Siemens BSC BR7, it has paging capacity about 270.000 paging/hour per LAC in 1 BSC.
You could check the counter Total Paging transmitted, is it reach 80% of maximum paging or not.
Or you could verify the other KPI like SDCCH Success Rate and TCH Blocking rate, because it affect Paging Success Rate