So far none of our Hiper series of products will support 500-700W power level. Best approach is probably to use PFS boost power factor followed by either TFS-2 2-switch forward or LCS LLC converter.
PFS-4 series will get you 400W universal input capability or 500W high line-only.

The bottleneck is in the DC-DC converter following the PFS boost PFC stage. TFS -2 series is limited to 340W continuous, and LCS series is limited to 440W.

In summary, you could get around 400W with PFS-4 boost PFC stage followed by LCS DC-DC stage with universal input or 440W with high line only (180-265VAC).

DER-484 is a design example using PFS and TFS-2 for ~300W output power with universal input. That particular design is configured as a battery charger. For straight 15V output, a much simpler output regulation circuit using a TL431 would be sufficient.