See this blog post
for an explanation of file sizes and the relationship to RAM sizes.
QVDs are uncompressed, so a 7GB QVD will require at least 7GB of RAM, so your RAM usage look reasonable.
To reduce the RAM requirements, you'l want to reduce the size of the fields in the QVD. You can do this by reducing the cardinatility -- the number of unique values -- of fields. For example, splitting timestamps into seperate Date and Time fields.
There are two tools you can use to identify field sizes.
1. Create a mem file and process with QV Optimizer. You can find a copy of QV Optimizer on the Forum.
2. Use the DocumentAnalyzer tool (http://robwunderlich.com/downloads/) against the consuming QVW. DocumentAnalyzer will identify the field sizes, and will also identify what fields are unused in your screen objects. You may be able to reduce the QVW RAM requirements by dropping unused Fields.