Revised GA drawings of Thermosyphone pot uploaded (file name-Thermosyphone pot GA drawings_R2) for your review.
DN15 size connection from vessel to seal  is OK.
"While Positioning both seal vessels (Thermosyphone pots) above the ATFD-H unit, please ensure the distance between Seal housing & bottom of the seal vessel is min. 650mm & max. 1000mm  with minimum bends & fittings in seal cooling lines."