Sometimes i have seen SharePoint performance issue at the client side - this can be due to many reason but you can give a try for below steps at client side and see if this helps you !
1. Close SharePoint
Designer.
2. Clear your
Internet Explorer's temporary Internet cache and close the browser.
3. Remove content in
Folder %System Drive%\Users\%user%\AppData\Local\Microsoft\WebSiteCache).
4. Type %temp% at a
run prompt and delete all the temp files in there.
5. Type temp at a
run prompt and delete all the temp files in there.
6. Delete
%APPDATA%\Microsoft\SharePoint Designer\ProxyAssemblyCache
7. Delete the
contents of: %APPDATA%\Microsoft\Web Server Extensions\Cache
8. Delete contents
of %USERPROFILE%\AppData\Roaming\Microsoft\SharePoint Designer
you can also check @ server side - change with your URL
$app = Get-SPWebApplication
http://abhi.interest.com
$app.ClientCallableSettings.ExecutionTimeout
Try to increase ClientCallableSettings.ExecutionTimeout values -
$app.ClientCallableSettings.ExecutionTimeout
= 5400000000
$app.Update()
Best of LUCK!
