First, as mentioned in the comment, check your data source. In SSRS, r-click on the data source, and select properties. In the properties dialog, check the "connection type". With a value of rsssharepointlist in the dataset, I'm guessing you're using a sharepoint list data source.
If you're using the SharePoint list data source, one consideration is that you can't select which view to use; it uses the default view. So if you list has thousands of items, but the default view for the SharePoint list has a filter to only show the 10 most recent items, then your report will show the 10 most recent items.
If you're using the xml data source, you're likely running into the fact that the SharePoint REST services use paging. I don't know what the solution in SSRS would be for this, other than to write a separate web service that does the call, iterating through each "skiptoken" that part of each batch of rows that points to the next set of rows. (the sharepoint rest service doesn't send all rows. It sends a batch of rows, along with a "skiptoken" field that has the url to retrieve the next batch.)
Also, perhaps check into joining the lists via a REST operation, instead of the lookup function.
Or, perhaps use something like SSIS to get the data to a database table. After all, 150,000 rows is a large list, but a small table. Trying to join that many rows via a function in an SSRS report is going to cause some sort of issue, timeout issues if nothing else.