Why is RoboHelp sluggish while editing text?

I upgraded to RoboHelp 2015 from RoboHelp 10 and I am experiencing sluggishness while editing text, opening topics, and everything else. It is very frustrating to the point of being unusable. This is in the same project I was working on in RoboHelp 10. Other applications, such as Captivate, are working fine.

Here are my system specs:

Operating System

    Windows 7 Professional 64-bit SP1

CPU

    Intel Core i5 660 @ 3.33GHz 

    Clarkdale 32nm Technology

RAM

    8.00GB Dual-Channel DDR3 @ 664MHz (9-9-9-24)

Motherboard

    Dell Inc. 0D441T (CPU)

Graphics

    DELL U2410 (1920x1200@59Hz)

    DELL U2410 (1920x1200@59Hz)

    1024MB NVIDIA GeForce GT 330 (Dell)   

Storage

    232GB Western Digital WDC WD2500AAJS-75M0A0 (SATA)  

Optical Drives

    TSSTcorp DVD+-RW TS-H653G

Audio

    Realtek High Definition Audio