Proposal to remove the limit of 15 max values for multiple values can also be retrieved from url in reports
We send the parameters as string so that multiple values can also be retrieved from url in reports for e.g url like - "memtype_in=in&memtype_value=1,2,3
However, there is a restriction for 15 values esp when you search for activity types which can be numerous. In this this case, if the values exceeds 15 the criteria are not respected.
Proposal to remove the limit of 15 max values. https://github.com/civicrm/civicrm-core/blob/master/CRM/Report/Utils/Get.php#L173