Which bag will be warmer, this bag or the Lamina -30 synthetic bag?

Tech Specs:

Material:

[Shell] 30D micro ripstop; [Lining] 30D nylon taffeta 

Insulation:

600-Fill down 

Shape:

Mummy 

Draft Collar:

Yes 

Max User Height:

[Reg] 78in (198cm); [Long] 84in (213cm) 

Shoulder / Hip / Foot Circumference:

[Reg] 62 / 58 / 38in ( 157 / 147 / 97cm); [Long] 64/ 60 / 40in (163 / 152 / 102cm) 

Stuff Size:

9 x 18in (23 x 46cm) 

Stuff or Storage Sack:

Both 

Degree:

-15F (-26C) 

Weight:

4lb 1oz (1860g) 

Recommended Use:

Mountaineering, winter camping 

Manufacturer Warranty:

Lifetime