Complex sentence: By 1915, with Tesla's debt at the Waldorf-Astoria being around $20,000 (about $400,000 in 2009 dollars) and unable to make any further payments on the mortgages, Boldt foreclosed on the Wardenclyffe property.
Split into simpler sentences: By 1915, Tesla's accumulated debt at the Waldorf-Astoria was around $20,000 (about $400,000 in 2009 dollars). When Tesla was unable to make any further payments on the mortgages, Boldt foreclosed on the Wardenclyffe property.