Elmet

Hello, looking for advise on process or products that will create a smooth transition between a new porcelain patio and existing slabs. Recently I had a rear extension, I opted for a concrete base, levelled and at the correct fall as was offered when pouring the oversite. This would be a temporary patio and in the spring, will be primed, adhesive and porcelain slabs used. The issue I have is the concrete surface is the same height as the existing slabs owned by a neighbour, when I use adhesive 15mm and porcelain slabs 20mm I am going to have a ~35mm step when walking through my garden gate. This is the only point it will be noticed but this small step will simple be a trip point. Any ideas what I could do to ensure a smooth(er) transition? I am open to ideas using borders etc. I am unable to raise the existing slabs. Images below are of the gate area, the yellow slabs are existing. The slate chips are just to fill the gap between.