Kerchoff's Current Law (KCL)states that the algebraic sum of the currents entering a junction must equal zero. The sum of the currents entering a junction ie equal to the currents leaving the junction. With voltage constant, the VA is perportional to the currents. If the supply voltge is 24V the max supply current for a 15va output is is 0.626A. The load elements on each branch of the parallel circuit are 7va and 8va which would draw 0.292A and 0.333A. The total load currents accoding to KCL is 0.625A. So in theory yes the output va will support the load.
However, if the load elements have an inrush current at any point in the loading then the output limit may be exceeded.
Most of the information about the Metasys System can be located at this link. http://cgproducts.johnsoncontrols.com/default.aspx?topframe.aspx&0
[This message has been edited by Ray97502 (edited 07-22-2005).]