WARN Document Vector 0:148 Table spec file is 35 MB large - this may result in increased memory consumption (path '\KNIME\BOW Clustering\Document Vector (#148)\port_1\spec.xml')
does this cause any problems?
It just tells you that the table is quite large and will use more memory.
If you want to save memory for these large documents/tables you can switch the memory policy to “write tables to disc” which will save memory but will use disc space instead (which will be slower an memory)