I am new to Qwt and Qt and require using Qwt to draw a minimum of 15 plots, ...
Guess you mean one plot with a minimum of 15 curves ?

...however I needed to fix the size of the qwtplot.
The legend is part of a QwtPlot widget - guess you mean you want to have a minimum size for the plot canvas. If true the ratio parameter of QwtPlot::insertLegend might be what you are looking for.

The large number of plots thus results in a large legend accompanied by a scrollbar which is undesirable.
And what type of legend would you like to have instead ?

I would further like to access individual legendItems to use their signals (clicked()) in order to highlight individual plots.
See:

Qt Code: 
  1. QwtPlot::legendClicked( QwtPlotItem * );
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Uwe