If you are troubling the issue of reducing the OST file size, you can easily solve the problem through using BLR OST to PST converter software. If you will use this software, it provides you with a free demo version to use it and also allows you to save the 15 email data from each and every folder of the OST mailbox. During the conversion Outlook is not required in your systems. I will suggest you use the software and recommend it to other users.

# No Limitation on File Size, you can Export Large OST to PST file
# 100% Safe, Secure and Fast Conversion Process
# Available Free Version to Test Software Functions
# Support all Outlook and OS Versions