Sandbox

SELECT 
  cscart_product_feature_variant_descriptions.variant, 
  cscart_product_feature_variants.variant_id, 
  cscart_product_feature_variants.feature_id, 
  cscart_product_features_values.variant_id as selected, 
  cscart_product_features.feature_type, 
  cscart_seo_names.name as seo_name, 
  cscart_seo_names.path as seo_path 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'en' 
  INNER JOIN cscart_product_features_values ON cscart_product_features_values.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_features_values.lang_code = 'en' 
  AND cscart_product_features_values.product_id = 101 
  AND cscart_product_features_values.feature_id = cscart_product_feature_variants.feature_id 
  LEFT JOIN cscart_product_features ON cscart_product_features.feature_id = cscart_product_feature_variants.feature_id 
  LEFT JOIN cscart_seo_names ON cscart_seo_names.object_id = cscart_product_feature_variants.variant_id 
  AND cscart_seo_names.type = 'e' 
  AND cscart_seo_names.dispatch = '' 
  AND cscart_seo_names.lang_code = 'en' 
  AND (
    cscart_seo_names.company_id = 1 
    OR cscart_seo_names.company_id = 0
  ) 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (15, 16, 17) 
GROUP BY 
  cscart_product_feature_variants.variant_id 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant

Query time 0.00058

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_product_features_values	range	PRIMARY,fl,variant_id,lang_code,product_id,fpl,idx_product_feature_variant_id	idx_product_feature_variant_id	12		3	Using where; Using index; Using temporary; Using filesort
1	SIMPLE	cscart_product_feature_variants	eq_ref	PRIMARY,feature_id	PRIMARY	3	cscart_dev_4_16.cscart_product_features_values.variant_id	1	Using where
1	SIMPLE	cscart_product_features	eq_ref	PRIMARY	PRIMARY	3	cscart_dev_4_16.cscart_product_features_values.feature_id	1
1	SIMPLE	cscart_seo_names	ref	PRIMARY,dispatch	PRIMARY	206	cscart_dev_4_16.cscart_product_features_values.variant_id,const,const,const	1	Using where
1	SIMPLE	cscart_product_feature_variant_descriptions	eq_ref	PRIMARY	PRIMARY	9	cscart_dev_4_16.cscart_product_features_values.variant_id,const	1	Using where

Result

variant	variant_id	feature_id	selected	feature_type
16GB	45	17	45	S
2.4"	77	16	77	S
Nokia OS	76	15	76	S