Have you upgraded to the newest version of google spreadsheets? We were having some performance issues that sound just like what you're experiencing and as soon as we made the switch, our sheets were super fast.
As far as I observed, latest big update improved the performance of large sheets a lot. Plus, using chrome is also making some positive difference. However, copying and pasting large data is still a problem. Instead I recommend to use copy to option within google drive.
The best was definitely the remove of cell limits and row limits. If I remember correctly, it used to be at 50k linrs , which you reach in no time. The new spreadsheets are way faster indeed!
New limits are here:
https://support.google.com/drive/answer/37603?hl=en
Number of cells: 400,000 total cells across all sheets - this is the one i don't like. If you log substantial amount of columns, it fills up pretty quickly
Number of columns: 256 columns per sheet
Number of formulas: 40,000 cells containing formulas across all sheets
Number of tabs: 200 sheets per workbook
GoogleFinance formulas: 1,000 GoogleFinance formulas
"All spreadsheet limits mentioned above have been removed in the new version of Google Sheets. The new version of Google Sheets should support 2 million cells of data, though please note that extremely large spreadsheets may have slower performance. Learn more about switching to the new version of Google Sheets."
I've tried copying a problem sheet to a new file and first impressions are positive. Thanks.